Acromion Index in Korean Population and Its Relationship with Rotator Cuff Tears

BACKGROUND Among the many causes of rotator cuff tears, scapular morphology is associated with the accelerating degenerative process of the rotator cuff. Acromion index (AI) was previously introduced and compared in two populations. METHODS We enrolled 100 Korean patients diagnosed with full-thickness rotator cuff tears by magnetic resonance imaging and intraoperative arthroscopic findings between January and December 2013. Another 100 Korean patients with an intact rotator cuff tendon identified on magnetic resonance imaging and other shoulder diseases, such as frozen shoulder and instability, were enrolled as controls. We retrospectively compared these 100 rotator cuff tear patients (mean age, 63 years) and 100 controls (mean age, 51 years) in this study. Two independent orthopedic surgeons assessed the AI on radiographs. We performed an interobserver reliability test of the AI assessment, and then compared the AI between two groups. RESULTS The measurement of the AI showed excellent reliability (intraclass correlation coefficient, 0.82). The mean AI in the rotator cuff tear group was 0.68 and it was significantly different between groups (p<0.001, 95% confidence interval). The AI was not related to tear size. CONCLUSIONS Our study showed that the AI was an effective predictive factor for rotator cuff tears in a Korean population.